It is well known in the industry to manufacture bullets and corresponding cartridge cases from either brass or steel. Typically, industry design calls for materials that are strong enough to withstand extreme operating pressures and which can be formed into a cartridge case to hold the bullet, while simultaneously resist rupturing during the firing process.
Conventional ammunition typically includes four basic components, that is, the bullet, the cartridge case holding the bullet therein, a propellant used to push the bullet down the barrel at predetermined velocities, and a primer, which provides the spark needed to ignite the powder which sets the bullet in motion down the barrel.
The cartridge case is typically formed from brass and is configured to hold the bullet therein to create a predetermined resistance, which is known in the industry as bullet pull. The cartridge case is also designed to contain the propellant media as well as the primer. However, brass is heavy, expensive, and potentially hazardous. For example, the weight of 0.50 caliber ammunition is about 60 pounds per box (200 cartridges plus links).
The cartridge case, which is typically metallic, acts as a payload delivery vessel and can have several body shapes and head configurations, depending on the caliber of the ammunition. Despite the different body shapes and head configurations, all cartridge cases have a feature used to guide the cartridge case, with a bullet held therein, into the chamber of the gun or firearm.
The primary objective of the cartridge case is to hold the bullet, primer, and propellant therein until the gun is fired. Upon firing of the gun, the cartridge case seals the chamber to prevent the hot gases from escaping the chamber in a rearward direction and harming the shooter. The empty cartridge case is extracted manually or with the assistance of gas or recoil from the chamber once the gun is fired.
One of the difficulties with polymer ammunition is having enough strength to withstand the pressures of the gases generated during firing. In some instances, the polymer may have the requisite strength, but be too brittle at cold temperatures, and/or too soft at very hot temperatures. Additionally, the spent cartridge is extracted at its base, and that portion must withstand the extraction forces generated from everything from a bolt action rifle to a machine gun.
Hence a need exists for a polymer casing that can perform as well as or better than the brass alternative. A further improvement is the base inserts to the polymer casings that are capable of withstanding all of the stresses and pressures associated with the loading, firing and extraction of the casing.